The Fair Labor Assn. said Thursday that it had conducted a thorough inspection of three factories in China operated by Foxconn, a major supplier, and had secured “groundbreaking commitments” that will reduce working hours, improve health and safety conditions and “establish a genuine voice for workers.” The group said it would continue to monitor the factories.

The nearly monthlong investigation, initiated by Apple and its suppliers, was a response to widespread criticism after worker deaths and injuries at the Chinese factories, which produce iPhones and iPads.

The Fair Labor Assn., an industry-funded group, said it found excessive overtime and problems with overtime compensation; several health and safety risks; and crucial communication gaps that have led to a widespread sense of unsafe working conditions among workers.

"The Fair Labor Assn. gave Apple's largest supplier the equivalent of a full-body scan through 3,000 staff hours investigating three of its factories and surveying more than 35,000 workers,” said Auret van Heerden, chief executive of the Fair Labor Assn. “Apple and its supplier Foxconn have agreed to our prescriptions, and we will verify progress and report publicly.”

The investigation found that within the last 12 months, all three factories exceeded both the group’s standard of 60 working hours per week (regular plus overtime) and the Chinese legal limits of 40 hours per week and 36 hours maximum overtime per month.

During peak production periods, the average number of hours worked per week exceeded 60 hours per worker. There were periods in which some employees worked more than seven days in a row without the required 24 hours off, the association said.

Foxconn said it has committed to bring its factories into full compliance with Chinese legal limits and Fair Labor Assn. standards on working hours by July 2013.